Engelen, D. “F. Hoekstra, In Dienst Van De BVD. Spionage En Contraspionage in Nederland”. BMGN - Low Countries Historical Review 120, no. 4 (January 1, 2005): 698–699. Accessed November 21, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-107258.